The invention relates to transmissions and, more particularly, to two-speed transmissions for marine propulsion devices and the like.
The thrust requirement curve (thrust vs. speed) for planing boats propelled by an outboard motor or a stern drive propulsion unit has a marked hump at the point where the boat is starting to plane. The propeller ordinarily must absorb full engine power at rated engine r.p.m. and maximum boat speed. A conventional size propeller normally limits the r.p.m. during this critical time, thereby limiting the thrust developed. If the propeller is designed to permit the boat to "go over the hump" under relatively high load conditions, such as when water skiers are being towed, it will permit the engine to run at excessive speeds once the boat is planing and less power is required to drive the propeller.
This problem could be alleviated by using a propeller having an adjustable pitch; however, many years of development have failed to produce a practical and efficient adjustable pitch propeller.
Also, it is desirable for propulsion units used in racing boats to have a transmission which permits the boat engine to rapidly turn up to a full speed when accelerating out of a turn and then shift automatically to facilitate full speed operation after the boat is planing.